1. Field of the Invention
The present invention pertains to a one-step process for the emulsion polymerization of vinyl chloride.
2. DESCRIPTION OF THE Prior Art
The use of conventional straight chain surfactants, e.g., sodium lauryl sulfate, in the emulsion polymerization of vinyl chloride will generally result in the formation of very small polymer particles unless the quantity of surfactant is carefully controlled by an incremental feed technique. One common way in which larger particles of polyvinyl chloride can be obtained is by first forming a "seed" particle of the polymer in an initial polymerization procedure, followed by a second polymerization or "seed growth" step. Some recently issued U.S. patents which relate to this seed growth technique are U.S. Pat. No. 3,383,346 to E. S. Smith, U.S. Pat. No. 3,642,740 to J. K. Pierce, Jr. and U.S. Pat. No. 3,755,225 to J. K. Pierce, Jr. et al. The effect of a mixed emulsifier system of a conventional surfactant and an alcohol during only the second step of such a process has been studied in the scientific literature, J. Ugelstad et al. J. Polymer Sci., Symposium No. 42, 473-485 (1973).
In addition to the foregoing prior art, the presence of various alcohols, such as stearyl alcohol, as a component in a polymerization reaction medium has been studied by other investigators. For example, U.S. Pat. No. 3,324,097 to G. E. A. Pears and U.S. Pat. No. 3,654,248 to E. Iida et al., relate to a polymerization system wherein a homogenized vinyl chloride monomer is polymerized in the presence of an oil-soluble catalyst in a suspension polymerization procedure. When such a system is used a mixture of emulsion and suspension polymerized polyvinyl chloride particles are formed. The effect of a mixed emulsifier of surfactant and alcohol in a one-shot polymerization of styrene has also been studied: J. Ugelstad et al., Die Makromolekulare Chemie, Vol. 175, pp. 507-521 (1974); J. Ugelstad, J. Polymer Science, Polymer Letters, Vol. 11, pp. 503-513 (1973), and A. R. M. Azad et al., ACS Polymer Reprints, Vol. 16, No. 1, pp. 131-142 (April 1975).
Alkyl phosphate surfactants have been proposed as primary emulsifiers in the emulsion polymerization of vinyl chloride in a seed technique, British Pat. No. 1,142,425 to Stauffer Chemical Company. They have also been proposed as emulsifiers in emulsion polymerization procedures in conjunction with monomer-soluble initiators in order to obtain a product having a highly porous configuration in the form of aggregates, U.S. Pat. No. 2,843,576 to J. H. Dunn et al.
It has not, however, been appreciated hitherto that a one-step polymerization procedure for vinyl chloride monomer can be achieved using a water-soluble initiator and an aqueous mixed emulsifier system containing a straight chain alkyl or alkenyl phosphate surfactant.